DY, BRITISH COPEPODA. 
three) wart-like, setiferous processes. Second pair 
sometimes foot-like, but mostly forming a strong pre- 
hensile uncinate hand. First pair of feet mostly 
(though not always) different from the following pairs 
and converted into a prehensile apparatus; second, 
third, and fourth pairs adapted for swimming; fifth 
pair 2-jomted, foliaceous; different in the two sexes, 
the basal joint usually dilated and more or less embrac- 
ine the smaller apical joint. Hyes as in Cyclops. 
Heart wanting. Copulative organs in the female 
symmetrical, in the male usually asymmetrical. Ovisac 
in most cases single, rarely double. 
This family, according to the arrangement here 
adopted, contains thirty-three genera* and eighty-one 
species, and is therefore by far the largest of the nine 
families coming within the range of the present Mono- 
oraph. The lmits of the family are precisely those 
adopted by Claus and Boeck, except that the group 
erected by the former author into a separate family 
under the name Pelicdide are here (as also by Boeck) 
included amongst the Harpacticide. There is, in 
fact, no important structural difference between the 
two, the point relied on by Claus as distinctive being 
the flattened form of the Peltidide, which is of no 
great importance in itself, and is found in certain 
Species of some genrea (e.g. Thalestris), the normal | 
form of which is cylindrical. The cylindrical form, 
with an abdomen not much narrowed, and not mark- 
edly distinct from the cephalothorax, must, however, 
* Excepting Cylindropsyllus, which cannot at present be referred 
with certainty to any family. 
